The invention relates a wiper device for motor vehicle windshields An oscillating wiper device is known (US-PS 25 05 078) in which a central plane which passes through the wiper blade extends vertically on the windshield when the wiper blade placed on the windshield is not loaded. This wiper blade is capable of cleaning a planar windshield in an optimal manner, since the relations between the wiper blade and the windshield remain constant along the wiping field brushed over by it--on both the forward and return paths--that is, no deviations from the normal line occur. In spherically curved windshields, on the other hand, the slope of this central plane relative to the windshield surface changes constantly as seen along the entire wiping field. This change also varies as seen in the longitudinal direction of the wiper blade when the wipers are driven so as to oscillate, which wipers brush over a wiping field on the windshield, which wiping field is similar to a ring segment. The position of the plane relative to the windshield area penetrated by it is different at the outer curvature of the wiping field than on its inner curvature and is in turn different than at a center curvature which is described in operation by the link between the wiper blade and the wiper arm. In spherically curved windshields, the optimal alignment of the surface relative to the windshield described in the planar windshield can only be achieved in a punctiform manner and in such a way that it wanders constantly in the longitudinal direction of the wiper blade during the operation of the wiper blade. In so doing, the deviations from the ideal in the more sharply curved side areas of the windshield are greater than in the more planar windshield central areas. The flexibility of the wiper rubber can only partially compensate for these deviations.
Therefore, in the known oscillating wiper devices (DE-OS 34 26 607), the oscillating axis was previously adjusted relative to the windshield contour in such a way that the position of the central plane relative to the windshield area penetrated by it, which position comes closest to the ideal state, is achieved approximately in the center position of the wiper blade. The greater the curvature of the windshield as seen along the entire wiping field, the greater the error of deviation from the ideal position of the plane; this error is designated as the deviation from the normal line and is expressed in angular degrees. For the reasons explained above, the deviation from the normal line at the inner circle, the central circle and the outer circle constantly differs in magnitude. It also follows from the discussion above that the angle, at which a line situated in the described plane deviates from a vertical line on the windshield area penetrated by the line, is designated as the deviation from the normal line. Another difficulty also results in that the described relations in the forward path of the wiper blade deviate from those resulting during the return path of the wiper blade. The conditions which occur in so-called single-lever wiper systems are particularly difficult to master, since the wiper blade must treat both sharply curved side areas of the windshield.